Diammonium monoalkali ferricyanide



June 6, 1944. R. B. BARNES ET Al.

DIAMMONIUM MONOALKALI FERRICYANIDE Filed March 13, 1943 @n./afrp/f ra a.

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ATTORNEY Patented June 6, 1944 nrAMMoNIUM MoNoALKALI FEmtIcYANlnE Robert B. Barnes and Leonard P. Moore, Stamford, Conn., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine Application March 13, 1943, Serial No. 479,027

(Cl. ,Z3- 77) 2 Claims.

The present application is related to copending application,Serial No. 318,896, filed February 14, 1940, directed to methods of producing diam- -monium monoalkali metal ferricyanide.

The present invention relates to diammonium monoalkali metal ferricyanide per se, as a new chemical compound.

A solution containing alkali metal ferricyanide may lbe readily obtained by chlorinating a solution of the correspondingv ferrocyanide. As a result of this chlorination procedure, the final solution contains alkali metal chloride as a, natural consequence of the reaction. Relatively pure crystals of alkali metal ferricyanide may be obtained from such solutions by suitable fractional crystallization through cooling or evaporation -or both.

It has been determined that whenevera soluble ammonium salt is added to a solution of an alkali metal ferricyanide, diammonium monoalkali metal ferricyanide forms, and Where the soluble ammonium salt is added in excess of that necessary for a metathetical reaction, there may exist in this reaction mixture unreacted alkali metal ferricyanide, unreacted original-ammonium salt, triammonium ferricyanide, monoammonium dialkali metal ferricyanide, and diammonium monoalkali metal ferricyanide. As to which One of these compounds may be most readily crystallized from the reaction mixturedepends upon their relative solubilities. That is, upon evaporation or cooling or both, thecompound least soluble will be precipitated.

When using a soluble inorganic ammonium salt, the diammonium monoalkali metal ferricy# anide is least soluble of those existing in the solution and, consequently, will be rst precipitated under proper conditions.

In practice, it is preferred to start with a solution of alkali metal ferricyanide containing some alkali metal chloride inasmuch as the desired double salt of ammonium is less soluble in such solutions containing alkali metal chlorides than in a solution containing alkali metal ferricyanide alone or in water alone. The invention contemplates, however, the use as an initial material of purebr relatively pure alkali metal ferricyanide in Water.

If the double salt of ferricyanic acid containing ammonium is to be used in the liquid state, a solution of a Water soluble inorganic ammonium salt may be added to the solution of the alkali metal ferricyanide or vice versa. The fact that such solutions also may contain unreacted alkali metal ferricyanide, triammonium ferricyanide and inorganic ammonium salts in many cases makes no difference. Such a situation is where the eventual solution is to be used in blueprint or other similar arts Where the light sensitiveness o1 the ferricyanic sale containing ammonium is of advantage. In other situations, however, where a pure or relatively pure ammonium alkali metal ierrc nide is desired fractional crystallization may be resorted to to recover the pure material substantially uncontaminated with other products.

In the latter case, that is, where crystalline material is desired and is to be obtained through levaporation and/or cooling procedures, it is decyanide is treated with a 25% caustic soda solution at from 18 to 65 C. for the purpose of ridding the solution of ferri ferro complexes, sodium ferrocyanide or'the like. The batch is then cooled to 15 C. and filtered to remove ferrie hydroxide, sodium ferricyanide and other insolubles. The pH of the filtrate is then adjusted to 8.5 with a mineral acid, preferably hydrochloric, and the resultant pre-treated solution is then satisfactory for the production of diammonium monosodium ferricyanide.

Where an initial alkali metal ferricyanide solution, pure or relatively pure, is available, this precaustic treatment may be omitted.

The sodium ferricyanide in solution is now reacted with a water soluble inorganic ammonium salt, preferably4 in solid phase. This solution of alkali metal ferricyanide, in order to insure an eflicient recovery of crystalline ammonium alkali metal ferricyanide per pass, should be reasonably concentrated as otherwise excessive cooling or evaporation or both will be necessary to recover a crop of double salt crystals. Where the mother liquor, however, drained from the double salt crystals, is recirculated, this is not so important, inasmuch as no substantial losses will occur.

As above stated, the initial solutionof alkali metal ferricyanide may be one obtained by dissolving that material in water to the proper concentration or it may be Va reaction mixture obtained from the oxidation as by chlorine of the corresponding alkali metal i'errocyanide. In any event, a solution containing at least 25 grams of alkali metal ferricyanide 'per 100 cc. is preferred. To this solution is added preferably a solid water soluble inorganic ammonium salt where eventual crystals are to be obtained, although Where a solution is to be used, the ammonium salt may be added dissolved in water.

For most eiiicient results, the liquid in the reaction vessel should be substantially saturated in order to insure an eicient crop of double ferricyanide crystals per pass. Ihis is indicated by `the fact that diammonium alkali metal ferricyanide is muh less soluble in saturated ammonium salt solutions at room temperature than in water alone or in a solution containing alkali metal ferricyanide.

While it is preferred that the liquid in the reaction vessel be maintained at substantially 25 C., thus not necessitating an articial cooling effect, yet temperatures above or below this may be used. If higher temperatures are used, a lesser amount of double salt crystals per pass will be obtained inasmuch as more of the salt remains in the mother liquor. If lower temperatures are used, a greater crop of final crystals will be obtained but at an added cost due to the artificial cooling effect.

It is preferred that the water soluble inorganic ammonium salt be added to the alkali metal ferricyanide in the molar proportions of 3:1. Use of more salt only slightly increases the yield but .contaminates the crystalline product with precipitated, unconverted salt, while use of less salt lowers the yield. a

While any alkali metal ferricyanide may be used as the starting material for the production of the ammonium alkali metal ferricyanide. yet that of sodium is preferred by reason of its cheapness. Any water soluble inorganic/ammonium salt may be used, such as the sulfate, nitrate and chloride, although the latter is preferred from the standpoint of cost.

The'contents of the reaction vessel where the double salt to be obtained is in crystalline form may then be either cooled or evaporated or both. Where cooling is resorted to, a temperature must not be reached which would cause precipitation of other compounds from the solution. For instance, where an initial reaction was obtained between sodium ferricyanide and ammonium sulfate so as to produce a saturated sulfate ferricyanide solution, when the reaction mixture was cooled to C., a copious crystallization occurred which, when subjected to microchemical tests, were determined to be sodium sulfate tinted with ferricyanide.

If the original ,reaction was carried out at 25 C., no cooling is necessary to obtain an initial crop of crude diammonium monoalkali metal ferricyanide crystals. However, cooling to C., insures a good crystallization eiect.

Evaporation may be resorted to for crystallization purposes and in such an event, it is preferred to blow a stream of warm air onto an extended area of the solution containing the reaction material.` Heating of the entire body `of the solution is generally undesirable due to the tendency of substances therein to decompose and also by reason of the fact that `such solutions must again be cooled, after concentration in order to avoid return of excessive quantities of the double salt in the mother liquor.

Slow evaporation of the saturated solution from the reaction vessel at room temperature leads to the growth of large cubical crystals of diammonium monoalkali metal ferricyanide measuring as much as one cm. on a side. If a current of warm air is ydirected normal to the surface of the non-agitated liquor, rosettes of crystals are formed, some of which may float on the surface, having a diameteras much as one inch.

In any event, evaporation or cooling may be continued as long as an analysis shows that the crop of crystalspbtained is free or substantially free from contaminating impurities. The magma is then filtered and the crude crop of crystals, Iafter being washed with liquor from a rst recrystallization, may be either used as such or recrystallized from water. The crude crystals analyze 94% (NH4)2NaFe(CN), 3% NHiCl and 2.2% NaCl. The mother liquor from the filtering operation may be returned to the reaction vessel or the initial cooler so that the values therein are not lost, and the process thus becomes cyclic.

The crude, anhydrous diammonium monoalkali metal ferricyanide crystals are then dissolved in water or liquor from a rst recrystallization so as to obtain a saturated solution at about 25 C. Upon cooling to 15 C., pure diammonium monoalkali metal ferricyanide is crystallized, which'was found to be a mixture of the anhydrous and dihydrated material equivalent to 1/4 H2O and containing less than 1% chlorides. After centrifuging, this once 'recrystallized material may then be air-dried and packaged.

The illtrate obtained by centrifuging the once recrystallized material may be returned to the cycle either to dissolve the crude anhydrous double salt or to a previous point.

For example, beginning with an aqueous solution of sodium ferricyanide. resulting from the chlorination of sodium ferrocyanide and containing approximately 30 grams of the former per cc. as well as from 5 to 6 grams of sodium chloride per 100 cc., there was added thereto at 25 C. a quantity of ammonium chloride in the molar ratio of 3:1 with respect to the sodium ferricyanide. Upon standing, a copious crop of crystals was obtained which were illtered from the mother liquor, the latter being returned to the cycle. A saturated solution of the crude material was made at 70 This solution was ltered and allowed to cool to room temperature. Small bright red crystals separated from the solution which were filtered oif and dried. Analysis showed 77% Fe(CN)E. This indicates 98.5% andhydrous (NH4)2NaF'e(CN).

The following approximate indices were determined on crystals in position of extinction:

Ni=1.595 N2=1.590 N3=1.586

These double ammonium alkali metal ferricyanide salts have been found to be of particular use in light sensitive work such as in the blueprint and photographic arts. They arev also useful as pigments in other words, due to the fact that ferricyanides lcontaining the ammonium radical have been found to produce more intense blues and alkali metal ferricyanides.

While the invention has been shown and described with'particular reference to specic embodiments, it is to be understood that it is not to be limited thereto but is to be construed broad- 1y and restricted solely by the scope of the appended claims.

What is claimed is:`

1. Diammonium monoalkali anide.

2. Diammonium monosodium ferricyanide.

metal ferricy- ROBERT i3. BARNES. LEONARD P. MOORE. 

